The present invention relates to improvements in spinning techniques for making yarns of fibres comprising an internal core, which yarns will be referred to in the following specification as "core spun yarns".
Numerous techniques have been proposed for making core spun yarns. The most wide spread technique in introducing a multifilament core into a rove during the last spinning operation, i.e. on the continuous filament to be spun, in which the core being introduced downstream of the last pair of rove-stretching rollers. This solution gives good results but has the drawback of being limited in speed, taking into account the fact that the yarn obtained is received by a system communicating a twist to the yarn for example a ring and traveller winding device.
U.S. Pat. No. 4,033,102 also proposes making self-twisted yarns of which at least one of the constituents presents a core in its central part, in which the core is likewise incorporated upstream of the last pair of rollers of the system for stretching a rove of fibres. This technique makes it possible to increase the speeds of production, taking into account the fact that reception of the yarns formed does not nessitate communicating a twist thereto. On the other hand, in the twist change zones, the yarn may sometimes present defects. Moreover, taking into account the fact that the yarn formed comprises at least two constituents twisted on one another, it is relatively delicate to obtain very fine yarns.
Numerous solutions which have heretofore not experienced industrial development have also been proposed for making spun yarns. For example, it has been envisaged to project elementary fibres onto a continuous yarn subjected to a momentary false twist upstream of the false twist spindle.
It has also been proposed to project the fibres onto a core previously sized or coated with a heat-sizing material. These solutions are relatively complex to carry out and do not lead to yarns having properties comparable to the conventional spun yarns having a real twist.